HTMLElement: tabIndex property

The tabIndex property of the HTMLElement interface represents the tab order of the current element.

Tab order is as follows:

1. Elements with a positive tabIndex. Elements that have identical tabIndex values should be navigated in the order they appear. Navigation proceeds from the lowest tabIndex to the highest tabIndex.
2. Elements that do not support the tabIndex attribute or support it and assign tabIndex to 0, in the order they appear.

Elements that are disabled do not participate in the tabbing order.

Values don't need to be sequential, nor must they begin with any particular value. They may even be negative, though each browser trims very large values.

const b1 = document.getElementById("button1");

b1.tabIndex = 1;